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The RF Workbench / Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter

« on: Today at 08:25 »

Congratulations on the license and becoming "official". I assume this means you are in the Netherlands or perhaps Germany. Maybe I will hear you on the air via SDR.

Also, to be clear, it's not clear to me that your problems were not the result of things external to the Class-D amplifiers you tried.

Yes I know there are also good class-D and bad AB amps. I just happened to have very good class-AB modules laying around, good for up to 150Watts and 20Amps of current. These can easily drive the RF output up to 100% modulation without any issues.

Im from Finland btw
My antenna is NVIS dipole, good for up to 1000km.

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The RF Workbench / Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter

« on: August 28, 2025, 0821 UTC »

Hmmm. What makes you think that a Class AB amplifier is "more robust" than a Class D? What makes you think that a Class AB modulator is "absolutely immune to RF" ?

Well at first I tested many Class-D modules. Some of them failed and some did not have very good response. Modulated RF output had some distortion (modulation triangle on my scope was rounded) at higher power levels etc oddities.
I have some Class-AB modules too so I tested them and all problems gone. Modulation is now very linear up to 100%.
Discrete Class-AB is just more robust anyway so I will keep it

Next month my transmitter will be on air on the weekends, just got my new licence.
(Radio Ambience, 6095kHz).

Last night I made some final adjustments and output power is now steady 130Watts @ 24Volt input.
Antenna is inverted V dipole.

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The RF Workbench / Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter

« on: August 24, 2025, 2224 UTC »

Hi,
I have built several U-LULU's using to-220 package IRF530 mosfets. RF signal source is external, adjustable duty cycles etc.
Modulator is class AB, because its more robust and absolutely immune to RF.
At 24Volt input, carrier power is 30-35Watts and PEP power around 120Watts. Output network is tuned to 6095kHz.
I changed the gate driver to ucc27531.
Mosfet stays cool but the output coil gets very hot, need to make new one with heavier wire.
However I have been using this many many hours at full power without other issues! Not bad for a single irf530 I think.